Process for desizing glass fabric



3,012,845 PROCESS FGR DESiZiNG GLASS FABRIC Edwin L. Lotz, Nutley, N.J.,assignor to Hess, Goldsmith 8: Company, incorporated, New York, N.Y., acorporation of Delaware No Drawing. Filed Aug. 31, 1960, Ser. No. 53,0347 Claims. (Cl. 8-438) This invention relates to a process for removingsize or binder material from an unfinished glass fabric, andparticularly to a continuous process for thermally desizing such afabric. Glass fabrics as the term is employed herein, refers to fabricsknitted, netted or woven in a definite pattern from yarns made up of anumber of filaments of glass, as distinguished from a randomdistribution of filaments as in glass wool.

Before individual glass filaments can be formed into strands and wovenor knit, for example, they must be coated with a sizing material whichserves as a continuous filament binder and affords a measure ofprotection to the filaments during weaving or knitting or subsequenttextile treatments. The sizing material lubricates the glass filamentsand the strands or yarns produced therefrom and allows them to slip overone another without undue abrasion and resulting breakage. The size isusually organic in nature, for example consisting of starch ordextrinized starch, gelatine, a complex amine, and in most instances alubricant such as mineral, animal or vegetable oil. The size, or bindermaterial as it is sometimes called,

is present on the fibers of the resulting glass fabric to the extent ofbetween about 1 and 4% by weight of the fabric, and must be more or lesscompletely removed from the fabric prior to coloring, when the fabricsare to be used for decorative purposes, or prior to the application of afinish in the case of industrial glass fabrics which are to be used withresins for the production of laminated or coated glass products. it isimportant that the fabric, particularly industrial fabric, be desized ina manner which reduces the original strength of the greige goods aslittle as possible. Unfortunately, every commercially acceptabledesizing technique does lower strength of the greige goods, but fabricstrength is restored to an appreciable extent, by application of afabric finish, forexample Volan or N .O.L.24, among many others, used inconnection with the finishing of industrial fabrics, and finish 140K fordecorative fabrics, all of which protect the yarn from self-abrasion.

Accordingly, in the desizing of the glass fabric as little strength aspossible should be sacrificed, as much of the size should be removed aspossible, that is to an ignition loss of less than 0.1% by weight of thefabric, and prefer ably between about 0.02 and 0.08%, and the desizedfabric should be as light in color as possible, preferably exceedinglywhite. It is entirely possible for two identical desized fabrics to havethe same ignition loss and yet one may be a light tan and the other anexcellent white as a result of different desizing techniques. The Whiterfabric is preferred for both decorative and industrial purposes.

By far the simplest methods and the ones in current use for desizingglass fabrics are thermal treatments, two of which are characterized bythe use of low temperatures and two by temperature sufficiently high tocause burning of the size at or immediately adjacent the sufface of thefabric. According to one low temperature method, referred to as thebatch oven process, the glass fabric is rolled up on perforated mandrelsand the resulting large rolls are placed in an oven which is maintainedat between about 500 and 700 F., and the size is slowly volatilized fromthe fabric. However, the total time in the oven ranges between about 55and 80 hours. While the batch oven technique thus consumes a veryappreciable amount of time, the desized fabric is white and has anignition loss of about 0.1%, which is considered quitesatisfactory.However, the tensile strength of the fabric is reduced by about 50%,which is somewhat below the strength reduction desired for industrialpurposes.

The other low temperature technique is a continuous treatment attemperatures sufficiently low to prevent burning of the size at thesurface of the fabric. However, the

thus treated fabric which retains a very high proportionof its initialtensile strength does so at the expense ofleaving on the heat treatedgoods a very large portion of the size in the form of a carmelizedresidue. While thiscontinuous low temperature desizing does not detractgreatly from the tensile strength of the greige fabric, retention ofstrength is attained at the expense of incom-. plete desizing. Not muchmore than about half of the size is removed and because of the highignition loss the thus treated fabric is not satisfactory for buildingglass laminates since the resins employed do not adhere well to thecarmelized surface coating.

Continuous high temperature desizing is referred to in the art asCoronizing. In one such process the glass fabric to be desized is passedin open width through a vertically or horizontally disposed furnace andsubjected;

to temperatures between about 1100 and'1500" E, with atmosphericconditions Within the furnace being such as to cause rapid burning ofthe size with a blue flame in a band across the fabric at or just abovethe fabric surface and very near the point of entry of the fabric intothe furnace. This continuous high temperature technique is described inKlug U.S. Patent No. 2,633,428 and in Waggoner U.S., Patent No.2,845,364, and is widely used in desizing glass fabrics to be used fordecorative purposes where hand and yarn set are the ultimate aim, andretention of original tensile strength is not so important. While theignition loss of the finished fabric is about 0.1% and the fabric isvery white, the tensile strength is very low, being only about from 30to 60% of that of the greige goods. Fabrics desized by this techniquethus do not exhibit the strength desired for industrial use s. v

A second high temperature desizing process is described, in Merrill R.May US. Patent No. 2,970,934, dated February 7, 1961. According to thatprocess a length of the fabric in open width is continuously passedthrough a furnace or thermal treating zone which ismaintained at asubstantially lower temperature, namely between about 900 and 1050" F.This lower temperature is sufficient to cause ignition and burning ofthe size on the surfaceof the fabric, but the process differs from thatof Klug-and Waggoner in control of the atmosphere within the treatingzone so that burning occurs at a point just inside the exit or dischargeopening of the furnace, and such burning is with a yellow flame, asdistinguished from the much hotter blue flame. The May process alsoproduces a de-, sized glass fabric with an ignition loss of about 0.1%,but the tensile strength of the desized fabric is between about 70 andof that of the greige goods. Thedesized fabric is a light amber or offwhite material.

It is an object of the present invention to provide a continuous hightemperature desizing process which will produce a desized glass fabrichaving a strength greater than that attained by the high temperatureblue flame method, and a fabric which is much whiter and has a lowerignition loss than that produced by the May process.

These and other characteristics which are highly desirable in desizeddecorative or industrial glass fabrics are achieved in accordance withthe present invention by heating a continuously advancing length ofsized unfinished glass fabric to a temperature sufficiently high tovolatilize the size from the fabric, and in fact to cause ignition ofthe size under certain conditions, and maintaining the fabric at suchtemperature for a time sufficient to volatilize a major portion of thesize, preferably in excess of 75% by weight of the size originallypresent on the fabric, while so diffusing the volatilized size as toprevent i-gnition and burning of the same adjacent the fabric, and thenraising the temperature of the partly desized fabric to a temperaturesufficiently high to set the fibers thereof, sometimes referred to assetting the weave, and maintaining the fabric at this elevatedtemperature to achieve the desired weave set and to volatilizesubstantially all of the sides remaining on the fabric, while preventingignition andburning of the volatilized size during raising of thetemperature and while the fabric is maintained at the higher or settingtemperature. It is indeed surprising that the present process whereincontinuous desizing is carried out at temperatures capable of ignitingand burning the size on or immediately adjacent the fabric is capable ofproducing a superior desized fabric product without ignition and burningof the size.

In an attempt to find an improved technique for continuouslydesizingglass fabrics and to examine the desirability of a vertical rnufiiefurnace for carrying out the process, I first examined the basicconcepts of high temperature desizing. Through infrared absorption testsit was established that at a temperature of about 1480 F., glass fabricabsorbs a maximum of thermal energy, and one would suppose that theradiating walls of a continuous desizing furnace should be maintained atthis temperature. Accordingly, a series of tests were carried out with avariety of fabrics at desizing temperatures of about 1480 F. While thesize was very efiiciently re moved from the fabric, the strength of thefabrics, as measured by the Mullen burst test after various periods ofexposure, deteriorated very rapidly, reaching a practical or'usefulminimum after five seconds exposure. After 14 seconds the glassexhibited Mullen. At 1360 F. Mullen strength fell off rapidly up toabout 20 seconds after which the strength remained constant. At 1300 F.a somewhat higher minimum was reached after 30 sec onds, while at 1200F. minimum Mullen strength was achieved after about 50 seconds exposure.In all of these tests thesize burned was a bright blue flame adjacentthe fabric shortly after the material entered the furnace. While theresults of'these tests definitely indicate that the ideal surfaceradiating temperature may be about 1480 F., at this temperature there isextreme physical damage to the fabric if it is allowed to remain at thattemperature for even 5 seconds. Maximum Coronizing temperatures incurrent use are between 1200 and about 1480" F.

From the above it can be seen that the fabric is very appreciablydegraded at these high Coronizing tempera tures. In tests carried out atthe lower temperatures of 1300 and 1350 F., with the size beingpermitted to burn on the surface of the fabric with a light blue flame,a medium weight casement fabric, designated Style 841, weighing 4.3ounces per square yard, constructed of warp and fill yarns comprising150 single end continuous filaments of a diameter between 0.0002 and0.0027 in., when coated with 140K finish exhibited a Mullen burstingstrength of only about 88 to 120. While the color and the ignition lossof the fabrics thus cleaned were acceptable,'the strength was not up toan acceptable level.

Proceeding on the assumption that the elevated temperatures and also theflame were responsible for the low finished Mullen strength, a series oftests were carried out on Style 841 fabric with the furnace maintainedat 1200-1250 F. under conditions which prevented the vaporized size fromburning adjacent the moving fabric. In these tests the fabric wasexposed to the aforementioned temperature for times of 7.3, 10.8 and 15seconds. The cleaned fabric coated with 140K finish exhibited Mullenstrengths of 116, 105 and 100, respectively. In each case the fabric wasat least as white or whiter than when desizing was carried out at 1350"F. with an exposure time of up to about 5 seconds with the vaporizedsize burning adjacent the fabric with a high blue-yellow flame, whichfabric exhibited a finished Mullen of only 88.

4 5' While these tests showed that lower temperature and elimination ofthe flame produced better results, they-,- also established that in theabsence of a flame it is possible to have prolonged exposure of thefabric at 1250 F. without substantial further reduction in physicalproperties.

Tests on another typical decorative fabric, Style 802, a light weightleno weave weighing only 2.03 oz./ sq. yd., substantiated the aboveobservations that once the size is properly removed, the elevatedtemperature can be sustained for additional periods withoutsignificantly decreasing the physical properties of the goods. Style 802was exposed in a pilot furnace having three temperature zones maintainedat 1100, 1260 and 1400 F. for a total of about 7.5 seconds. Subsequentruns were at exposure times of 12 and 1.5 seconds. Unfinished Mullenstrengths were 34, 33 and 31 lbs/sq. in;, respectively.

The above tests were all carried out in a pilot vertical muffle furnace6 feet in length, and in the runs at 1200-1250 F. considerabledifficulty was encountered while endeavoring to pass the fabric throughthe furnace without ignition and burning of the size at the surface ofthe fabric. Furthermore, in these tests, as in the prior art,particularly as evidenced by the Klug and Waggoner patents, the fabricat ambient or room temperature was introduced in open width directlyinto the furnace maintained at Coronizing temperatures somewhere between1100 and 1500" F., usually between about 1350 and 1480 F. The fabric isthus subjected to a very great thermal shock, it being raised fromatmospheric temperature to in excess of say about 1250 F. in the spaceof but a few seconds. Under such conditions the size volatilizes sorapidly, particularly at temperatures in the upper portion of the rangeabove specified, that it is exceedingly difi'icult to avoid ignition.Accordingly, it was decided to carry out desizing under conditionswhereby the fabric is gradually raised to the temperatures necessary toassure proper setting of the fibers or weave setting, usually about1250-1350 F., while also avoiding ignition and burning of the size inthe furnace.

The vertical pilot unit was modified to provide three two-foot sectionsor zones which were maintained at progressively higher temperatures. Thefabric was introduced at the top of the furnace in which the first zonewas maintained not above about 1100 F., the second or middle zone atbetween about 1100 F. and about 1280 F. and the third or bottom zone ata temperature above 1280 and up to 1350 F. When operating in thisfashion, astoundingly improved results both as regards the desizedfabric whiteness and the finished Mullen strength were. realized, asdescribed hereinafter.

Thus, in accordance with the process of the present invention, thefabric is continuously introduced into a first zone maintained'at atemperature sufficiently high to fairly rapidly volatilize the size,preferably above 800 F. but not above about 1100 F. In this zone thevolatilized size is so diffused, preferably with air, that burning whichis possible at temperatures between about 800 and 1100 F. is avoided,and then the fabric is introduced into another zone where it is raisedto proper weave setting temperatures, i.e. up to about 1400 F. and theremaining size is volatilized, but not permitted to burn adjacent thefabric in this other zone. While it is possible to carry out the presentprocess by first heating the fabric up to about 1100 F. and thensubjecting it to temperatures between about 1280 and 1400 F. in a secondzone, for example, it is preferred to employ one or more intermediatezones serving to gradually raise the temperature of the fabric to therange 1280-1400 F., thus avoiding the thermal shock which I have foundis detrimental to the material.

During initial heating of the fabric at least a major portion of thesize thereon is volatilized, and in most instances between about 75 and95% of the size is removed in this stage. During the initial heating orin the first heating zone the ignition loss of Style 841 greige fabricis preferably reduced about for example from 3.53% to about 0.33%,before the fabric is raised during subsequent heating to above about1100 F. I have also found that 'with certain of the heavier and bulkierfabrics, for example those weighing above about 6 ounces per squareyard, it is more important that a high proportion of the size be removedduring this initial heating than with lighter fabrics in order toachieve an excellent white color in the completely desized fabric. Forexample, with Style 978, a heavy boucl fabric weighing 9.22 ounces persquare yard and having an initial ignition loss of 1.91%, unless theignition loss is reduced to about 0.20% or below during initial heating,a very white product is not obtained. In like manner with Style 95919,another heavy boucl fabric, the ignition loss of about 2.4% ispreferably reduced to about 0.15% in the first zone. Thus, in order toachieve a desized fabric of excellent whiteness it can be said that aminimum of about 75% and in some cases about 85 to 95% of the size isremoved from the fabric in the first zone or during initial heating.

Burning of the size is avoided in the first zone by sodiifusing thevolatilized size as to produce a mixture of size vapor and air too leanto ignite and burn. This diffusion may be most simply effected byproviding an adequate draft through at least the first or fabricentering zone of the furnace, A major portion of the diffusedvolatilized size is desirably removed from the vicinity of the fabric inthe first zone, so that only a minor portion of the vapor producedtherein may enter the second and any subsequent zones of the furnace.Where the furnace is vertically disposed with the coolest zone at thetop and the fabric is passing downward the problem of diffused vaporsentering the second or subsequent hotter zones of the furnace does notexist.

Reference may be had to the application of Horace L. Smith, Jr.,entitled Muffie Furnace, Serial No. 53,192, filed on even date herewith,for a description and illustrations of a vertical mufiie furnaceparticularly adapted for carrying out the process of the presentinvention. The Smith furnace provides a muffie run comprising at leastthree heat treating zones, each of which are provided with vaporexhausting means.

While the novel desizing process of this invention has thus far beendescribed as the sequential heating of a glass fabric in two or threestages or thermal treating zones, the process may be carried out in amuffle furnace comprising but a single zone maintained at incrementallyincreased temperatures over its entire length, it being essential onlythat the fabric be subjected to gradually increasing temperatures andthat a major portion of the size be removed below about 1100 F. Forexample, in a vertical muffie with sized fabric entering at the lowerend the base ofthe furnace might be maintained at 900 F., but a foot ortwo above the base the temperature of the muffle may be 1000 F. and soon to the exit end of the muffie which might be maintained at 1400 F. Inmost instances it will be simpler from the point of view of furnacecontrol to carry out the process in a mufile having three sections thefirst maintained between about 800 and 1100 F., the second between about-0 and 1280 F., and the third from about 1280 to 1400 F. The temperaturedifferential between adjacent zones is not sufficient to adverselyaffect the fabric.

It is essential to the present process that a major portion of the sizebe removed below about 1100 F. and that ignition and burning of the sizebe avoided throughout the process. In the apparatus set forth in theaforementioned Smith application no auxiliary means such as a fan needbe provided for avoiding ignition in the second or third treating zones,although in some instances it may be desirable to provide an independentdraft in the zone subsequent to the initial heating zone to preventignition therein. In the Smith furnace, a major portion of the diffusedsize vapor is removed from the mufiie at the head of the first zone sothat the draft to the second zone plus the size vaporized therein doesnot produce an ignitible mixture in the second zone.

When three zones are employed, the second zone provides a very gradualtransition to the temperatures above about 1280" F. necessary to effectproper weave setting and fiber relaxation, which impart a desirable feeland hand to the desized fabric. In the second and third zones the sizeremaining on the fabric is substantially completely volatilized and thedesized fabric has an ignition loss between about 0.02 and 0.08%. Thedesized fabric is exceedingly white.

The first zone, maintained at temperatures up to about 1100 F. resultsin a substantially lower rate of volatilization of the size than occursin conventional Coronizing process, a rate sufiiciently low thatcombustion does not take place with a normal air draft which wouldsupport combustion at higher temperatures. In pilot plant operations andalso in a commercial installation employing the present process it hasnot been necessary to employ a forced draft in the first or fabricentering zone to avoid ignition and combustion of the size therein. Yet,I have found that at temperatures appreciably above 1100 F. in the firstzone, i.e. 1250 F. and upward normally employed in Coronizing,'burningof the size occurs regardless of the'manner in which the draftis'controlled.

The tests reported in the following Tables I-III are illustrative, ofthe present process, but are not intended to limit the scope of theinvention, neither do they necessarily present optimum operatingcondition for a commercial installation. Each test wascarried out in-asix foot vertical pilot mufile furnace, either withall of the furnacemaintained at the indicated temperature or divided into two or threesections of equal length as indicated by the temperatures and dwelltimes reported. In

Table l [Casement fabric style 841-4.3 ozJsq. yd. Warp and fill ECDE 1/01Z] Mullen Bursting rength Temp. Dwell Ignition (1b.,lsq. in.) Run F.)Time T oss Color (See) (Percent) Un- Finished finished (140K) Greige(untreated) 3. 53 1 1,020 7. 35 0. 13 Dark Tan. 2 1, 070 4 1, 350 4 0.04 Fair White.

1, 350 4 0.08 103 182 Excellent White. 1,020 7. 35 5 1,275 7 1, 350 70.07 50 D0. Present Standard 0. 04-0. 08 40 125 Fair White.

Product (Coronlzed with Flame).

7 some instances the fabric was introduced at the top and sometimes atthe bottom, but always to the zone of lowest temperature. The directionof fabric travel was found to have no effect upon the characteristics orprope'rties of the desized goods. In every case, unless otherwisespecified, desizing was effected without ignition and burning of thesize in the fabric treating muflle.

In run 1, which is not the complete process of this invention, thefabric was subjected to a temperature 1020 F. for 7.35 seconds. While adesized fabric exhibiting substantial strength was produced, its darktan color was not acceptable. In run 2, where the fabric was subjectedvolatilization of size from this medium weight Style 841" casementfabric was about the same at temperatures of;

1050 and 1275 F. On the basis of this information and 1 the data ofTable I, a commercial thermal desizing furnace, as described in theSmith application, having three foot sections or treating zones, andcapable of desizing Style 841 fabric at the rate of 60 yards per minuteis being operated with the first section at 1000" F., the second sectionat 1200 F. and the third section at 1350" F., with a dwell time in eachsection of about 7 seconds.

Table II reports tests conducted with heavier fabrics, namely bouclStyles 95919 and 978.

Table II [Bonel fabric style 05919-799 ozjsq. yd. Warp ECDE 150 l/O IZ:Fill RX 43 Ratine] Mullen Bursting trength Temp. Dwell Ignition (lb./sq.in.) Run 7 F.) Time loss Color (See) (Percent) Un- Finished finished(140K) Greige Goods (Un- 2. 41 480 treate Present Standard 0. 04-. 08102 Fair White.

Product (Coronlzed with Flame).

""""""""""" 1,275 Good White.

1, 350 Fair White. 1,040 3 1,275

1, 350 Excellent White.

[Bouel fabric Style 978-9.22 oz./sq. yd. Warp ECD 450 2/2: Fill RX 31ERatine] Greige Goods 1. 133

Present Standard 0.0%.08 90 Fair White.

Product (Coronized with Flame). p

"""""""""""" 1, 350 9. 7 0.17 55 105 Excellent White.

to temperatures of 1070 and 1350 F. for 4 seconds each a fairly whiteproduct was obtained which was substantially stronger than the presentstandard material. Good results were also obtained in run 3, but thewhitest fabric was obtained in runs 4 and 5, with run 4 being equivalentto 4 seconds at 1070 F. and 8 seconds at 1350 F. It is significant tonote that runs 4 and 5 both produced a superior white, as compared tothe standard product, and also gave an increased strength of about 46%and about 24%, respectively, over the material cleaned in the "standardfashion.

From information obtained in the series of runs reported in Table I itwas determined that the rate of Examination of run 2 shows that thepresent process produces a fabric of equal whiteness but having aphysical strength approximately 100% greater than the standardcommercial product. Run 3 produced a far superior White with a physicalstrength greater than the standard.

It will be noted that substantially longer dwell times are required atthe temperatures indicated to remove a substantially lesser quantity ofsize or hinder material from the heavier, more bulky fabric.

Table III reports the results of tests carried out with a heavyindustrial glass fabric, and Table IV the rate of volatilization fromthat fabric.

Table 111 [Industrial fabric HG639.76 oz./sq. yd. Thickness 0.14 in.Warp and fill: 16 X l il50S 4/2] Tensile Temp Dwell Ignition Run F.)Time loss Unfinished Volan Color (See) (Percent) Warp Fill Warp FillGreige Goods 2.2 308 279 1,020 7 1 1,280 7 1,350 7 0.06 130 I18 GreyWhite. 1,020 10 i 2 1, 280 10 1, 350 10 0. 05 103 199 128 Good White.1,020 15 a 1,280 15 1,350 15 0. 03 79 73 I55 131 Excellent White.

From Table IV it can be seen that the sizing material is very rapidlyvolatilized from the fabric at 1020" F., but once approximately 90% hasbeen removed equivalent treatments at 1280 and 1350 F. removes theremainder only with very great difficulty. Accordingly, a proper timesequence for a fabric such as PIG-63 is approximately 4 seconds at 1200F., 8 seconds at 1250" F. and about 15 seconds at 1300 F.

The tests above reported clearly indicated that the time of treatment isnot only dependent upon temperature but also upon the weight of thefabric and its weave, whether tight or loose. The quantity of size onthe greige goods is of course also an important factor, and it can beseen that one cannot predict the precise treating times required for allof the many fabrics encountered.

As a practical matter, a vertical furnace is preferred to a horizontallydisposed muffie since with the former it is possible to have a muchlonger thermal treating run without imposing undue tensile stress uponthe hot fabric or encountering sagging as in a horizontal furnace.

Thus in accordance with the present invention desizing is carried outwithout a flame and under initial heating conditions, preferably between800 and 1100 F. such that a major portion of the size, preferablybetween 75 and about 95%, is volatilized from the fabric and so diffusedas to prevent ignition of the same. The fabric is then gradually raisedinto the range of about 1280-1400 F. for substantially completevolatilization of the size and setting of the weave. By the method ofcontinuous desizing set forth herein a thermally desized fabric can beproduced which has a superior finished physical strength, for example,from about 20 to 100% greater, and a much whiter color as compared withcomparable materials desized by continuous high temperature techniquesemploying a flame to remove the size or binder material.

I claim:

1. A process for desizing a sized unfinished glass fabric, whichcomprises heating an advancing length of said fabric to a temperaturesufficiently high to volatilize the size from the fabric, maintainingthe fabric at such temperature for a time sufficient to volatilize atleast 75% of the size, so diffusing the volatilized size as to preventignition and burning of the same adjacent the fabric, raising thetemperature of the partly desized fabric to a temperature suflicientlyhigh to set the fibers thereof, and volatilizing substantially all ofthe remaining size from the fabric while diffusing the volatilized sizeto prevent ignition and burning of the same in the vicinity of thefabric at the elevated temperature.

2. A process for desizing a sized unfinished glass fabric, whichcomprises heating an advancinglength of said fabric to a temperaturesufficiently high to volatilize the size from the fabric, maintainingthe fabric at such temperature for a time sufficient to volatilize atleast 75% of the size, so diffusing the volatilized size as to preventignition and burning of the same adjacent the fabric, removingvolatilized size from the vicinity of the fabric, raising thetemperature of the partly desized fabric above about 1100 F. to set thefibers thereof, and volatilizing substantially all of the remaining sizefrom the fabric, while diffusing the volatilized size to preventignition and burning of the same adjacent the fabric during-raising ofthe temperature and while the fabric is at fiber setting temperature.

3. A process for desizing a sized unfinished glass fabric, whichcomprises gradually heating an advancing length of said fabric to atemperature sufficiently high to vo1a tilize the size from the fabric upto about 1100 F., maintaining the fabric at such temperature for a timesufficient to volatilize a major portion of the size, so diffusing thevolatilized size as to prevent ignition and burning of the same adjacentthe fabric, removing volatilized size from the vicinity of the fabric,gradually raising the temperature of the partly desized fabricsufiiciently to set the fibers thereof and not above about 1400 F., andvolatilizing substantially all of the remaining size from the fabric,while diffusing the volatilized size to prevent ignition and burning ofthe same adjacent the fabric during raising of the temperature and whilethe fabric is at fiber setting temperature.

4. A process for desizing a sized unfinished glass fabric, whichcomprises heating an advancing length of said fabric to a temperaturebetween about 800 F. and 1100 F., maintaining the fabric at suchtemperature for a time sufficient to volatilize between about and of thesize, so diffusing the volatilized size as to prevent ignition andburning of the same adjacent the fabric, gradually raising thetemperature of the partly desized fabric to between about 1280 F. and1400 F., and volatilizing substantially all of the remaining size fromthe fabric, while diffusing the volatilized size to prevent ignition andburning of the same adjacent the fabric during said gradual temperatureraising and while the fabric is at said latter temperature.

5. A process for desizing a sized unfinished glass fabric, whichcomprises continuously introducing an advancing length of said fabric toa treating zone maintained at a temperature between about 800 F. and1100 F., retaining the fabric in said zone for a time suflicient tovolatilize a major portion of the size, so diffusing the volatilizedsize as to prevent ignition and burning of the same adjacent theadvancing fabric, exhausting a major portion of the volatilized sizefrom said zone, subsequently introducing the advancing partially desizedfabric to another zone maintained at a temperature between about 1280 F.and 1400 F., and retaining the fabric in said other zone for a periodsufficient to volatilize substantially all of the size remaining on thefabric and to set the fibers thereof, while diffusing the volatilizedsize to prevent ignition and burning of the same adjacent the fabrictherein. 1

6. A process for desizing a sized unfinished glass fabric, whichcomprises continuously introducing an advancing length of said fabric toa treating zone maintained at a temperature between about 800 F. and1100 F., retaining the fabric in said zone for a time sufficient tovolatilize a major portion of the size, so diffusing the volatilizedsize in said zone as to prevent ignition and burning of the sametherein, exhausing a major portion of the volatilized size from saidzone, introducing the advancing partially desized fabric to a zonemaintained at a temperature between about 1100 F. and 1280 F.,volatilizing a major portion of the remaining size therein Whilediffusing the volatilized size to prevent ignition and burning of thesame adjacent the fabric therein, and then introducing the advancingfabric to a zone maintained at a temperature between about 1280 F. and1400 F. to set the fibers thereof and volatilize any residual size fromthe fabric.

7. A desized glass fabric product desized by the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS2,845,364 Waggoner July 29, 1958

1. A PROCESS FOR DESIZING A SIZED UNFINISHED GLASS FABRIC, WHICH COMPRISES HEATING AN ADVANCING LENGTH OF SAID FABRIC TO A TEMPERATURE SUFFICIENTLY HIGH TO VOLATILIZE THE SIZE FROM THE FABRIC, MAINTAINING THE FABRIC AT SUCH TEMPERATURE FOR A TIME SUFFICIENT TO VOLATIZE AT LEAST 75% OF THE SIZE, TO DIFFUSING THE VOLATIZED SIZE AS TO PREVENT IGNITION AND BURNING OF THE SAME ADJACENT THE FABRIC, RAISING THE TEMPERATURE OF THE PARTLY DESIZED FABRIC TO A TEMPERATURE SUFFICIENTLY HIGH TO SET THE FIBERS THEREOF, AND VOLATILIZING SUBSTANTIALLY ALL OF THE REMINING SIZE FROM THE FABRIC WHILE DIFFUSING THE VOLATILIZED SIZE TO PREVENT IGNITION AND BURNING OF THE SAME IN THE VICINITY OF THE FABRIC AT THE ELEVATED TEMPERATURE. 